Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin. Acetylcholine, gastrin, and histamine stimulate the proton pump in parietal cells to release hydrogen ions and decrease pH.
20kg piece of pure gold, i think........
B. chloroplast carrries out photo synthesis
The hormone calcitonin, which is produced by the parafollicular or C cells of the thyroid, has the opposite effect on blood calcium levels as does PTH. I hope this helps! : )
Examples:
Respiratory System, (I think) Organ System, Circulatory System, Nervous System, etc.